Alzheimer's disease is a 100% fatal neurodegenerative disease characterized by a chronically deteriorating course of cognitive, and later vegetative function. The definitive diagnosis of Alzheimer's disease is made by pathologic examination of postmortem brain tissue in conjunction with a clinical history of dementia. The diagnosis of definite Alzheimer's disease cannot be made in living patients as it requires examination of brain which cannot be performed in living individuals for ethical reasons. The diagnosis of definite Alzheimer's disease is based on the presence in brain tissue of extensive infestation by neuritic (senile) plaques and neurofibrillary tangles (NFT) whose density in brain are correlated with the severity of the clinical symptoms of the disease. The purpose of the present invention is to provide a laboratory based diagnostic test to allow the definite diagnosis of Alzheimer's disease in living patients by utilizing patient samples more accessible than brain.
Paired helical filaments are the only known pathological protein common to the two major neuropathological features which define Alzheimer's disease, neurofibrillary tangles and senile plaques. The biochemical characterization of paired helical filaments has been impeded because of technical difficulties in purifying and solubilizing this protein, a problem only recently solved. (Journal of Neurochemistry, Vol. 54, 148-155, 1990).
Postmortem detection of paired helical filaments (PHF) has been previously reported (Journal of the American Medical Association, Vol. 263, 2907-2910, 1990). This ELISA based test employing the antibody Alz50 may be used for the postmortem diagnosis of Alzheimer's disease. However, this test appears of no value for the diagnosis of Alzheimer's disease in living patients as it exclusively utilizes postmortem Alzheimer's brain samples.
Paired helical filaments purified and solubilized from Alzheimer's brain have been further characterized utilizing polyacrylamide gel electrophoresis (PAGE) which separates the PHF into: 1) a broad band of immunoreactivity ranging in molecular weight from approximately 20 to approximately 300 kilodaltons and 2) a specific 66 kilodalton protein referred to as PHF AD66 protein.
Others have attempted to clinically detect Alzheimer's disease in living patients. Such an attempt is disclosed in Wischik's European Patent Application WO89/03993. The specific protein detected using the Wischik method is believed to be a 9.5 kilodalton fragment of the 66 kilodalton protein obtained from PHF. This protein is different and physically separable from the material comprising the broad band of immunoreactivity, which serves as the basis for the present application. Wischik, in order to obtain his 9.5 kilodalton protein and corresponding antibody employed extensive and excessive digestion to solubilize his PHF. This apparently made the derived monoclonal antibody relatively unreactive. Thus, the test itself has never obtained clinical success.